Currently, helicopter is a typical example of vertical take-off and landing aircraft capable of generating lift without running on the ground. A helicopter has a large rotor, compared with its fuselage, and generates lift and thrust by rotating the rotor. There have also been known, though few in number of types, fixed-wing aircraft that perform vertical take-off and landing by changing the direction of the thrust derived from jet engines.
The fuselage of a helicopter has a relatively large size itself, and in addition, the helicopter is equipped with a main rotor larger in size than the fuselage and a tail rotor at the tail of the fuselage. Thus, if take-off, landing or attitude control is performed in a small space surrounded by obstacles such as buildings or trees, the main rotor or the tail rotor may come into contact with the obstacles. Accordingly, a large space needed for the take-off and landing.
In the case of a fixed-wing aircraft capable of vertical take-off and landing using jet engines, the jet exhaust is high in temperature and also the exhaust emission is large in volume. Accordingly, small objects such as stones are blown off by the jet exhaust during take-off or landing, possibly damaging surrounding buildings or the like. Thus, also in the case of the fixed-wing aircraft, a large space is needed for the take-off and landing.
There have already been proposed vertical take-off and landing (VTOL) aircraft capable of safe take-off and landing even in a small space (see Patent Documents 1 and 2, for example). The vertical take-off and landing aircraft disclosed in Patent Documents 1 and 2 are equipped with ducted fans having propeller type fans arranged within cylindrical ducts or nacelles.